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Spalted wood - general information

Before I go into this post about spalted wood I want to be sure that this is not interpreted as being smarter or a better woodworker than anyone else. Quite the contrary. Most of what I know about wood comes from doing things wrong. Since I work with wood 7 days a week I have utilized my opportunity to ruin quite a bit of really good wood. Eventually I catch on with things that occur regularly.

Spalted wood is wood that has started to decompose and has become inhabited by colonies of fungus. The fungus is what causes the atypical coloring. When 2 or more colonies of fungus come in contact with each other a black line will occur. This is a barrier between the colonies.

The further the spalting progresses, the more dramatic the random coloring and the further along the decomposition of the wood.

The wood will progress from slightly softer, to cork like, to crumbly when it has gone too far. Spalted wood to be stabilized is usually in the cork like stage. This is the time when the coloring is at it's peak and the wood still maintains a degree of structural integrity. This is the time when the wood is easiest to stabilize. Even by the do it yourselfers. The wood in this form easily accepts the stabilizing solution much like a dry sponge placed in a bowl of water.

The way stabilizing works is a stabilizing solution is used to impregnate the wood in a tank that is placed under a vacuum and pressure. After the wood is completely impregnated it is then heat cured causing the solution to catylize and become a solid. Properly done the solution will penetrate the fibers and pores of the wood giving it enhanced hardness and durability.

Stabilizing does not replace the wood so it is still subject to the original structural integrity. It has just been enhanced in multiples.

Even when stabilized, the 2 weakest woods will be heavily spalted pieces and end grain pieces. If you take either one of these types of wood at about 1 inch thick and attempt to break them in half, they will. If they don't, it just means you weren't trying hard enough.

With all this said, people might say "then why use the stuff?".
Answer: because it looks so good.

For those who insist upon using woods like this special care must be taken. Construction should be in a manner that would not subject the wood to flexing or side impact that would cause breakage. Sharp tools, low heat build up and slower speeds when drilling or grinding are critical. Spalted woods will usually have some small voids and irregularities that can require fills with CA glue for a more uniform surface and finish.

Sure it is extra work, but the dramatic results are more than worth the extra effort.

This photo is to show a piece of maple burl with spalting that has been stabilized. Prior to stabilizing the areas to the right where the wood is blonde and reddish are the areas that would have still been hard wood. The grays and browns would have been cork like. After stabilizing the wood now has a more uniform hardness and durability making it usable.

So you put it under low pressure (vaccuum) and then pressurize with the stabilizing solution? Thanks for the information. It cleared up several misconceptions I didn't know I had.

My stabilizing is all done by K&G in Arizona. They are thought of as one of the best.
I used to do my own where the wood went under a vacuum at 28+, this was followed by a few days at 80+ pressure, followed by heat curing.
I think the professionals like K&G and WSSI go a lot higher on the pressure.

Interesting article, having recently worked for the first time with some stabilised wood, I think it was from you in fact, it does work a lot differently to standard wood. Do you have any details around the chemicals used in the process?
I did a bit of mycology at uni and I seem to remember there are broadly 2 types of spalting:
bleaching by White rots that break down the lignin, and
pigmentation spalting where the hyphae grow into the wood cells giving a typically bluish colour.

The lines that form can be where two colonies meet or at the edge of the colony, it has a proper name that I can't remember....

When stabilising burrs will the solution act to glue any loose eyes in place?

Great summary, Mark, thanks! I love working with spalted woods, but I have learned over time to be much more selective and careful with them. The cross-cut or endgrain pieces are often the most spectacular looking ones, but the cut and the spalt can both be a risk for instability. Very often these pieces come back cracked from stabilizing - or even broken into pieces when the blank had hidden cracks that broke under pressure. I think Mario mentioned it somewhere, I have started to try and intentionally break all my blanks before I use them - with reasonable force. The unstable ones will usually show and I sort them out. Sometimes they break and I use the small pieces for ferrules or spacers, but several of my woods I have given up on. For example, spalted Hawaiian kukui nut is a beautiful wood if cross-cut, but it is extremely light and porous in its natural state. Almost all pieces I had stabilized cracked on me, so I only use it as ferrules at this time. In my general experience, denser woods like hard maple or signature are less problematic, although with everything in endgrain you should be aware of the risk.

I also find that stabilizing supports the structural stability of the wood, but it does not necessarily fill voids or cracks, especially not larger ones. So, woods like buckeye burl, which naturally has tons of voids, will still have them after stabilizing and it is better to fill them. In burl woods I find that stabilizing may help a bit but it definitely does not fill all the rooms between eyes, so sometimes the handles have little grooves in them when they are finished. As long as I think they are overall stable and the grooves/voids are not too large, I call it character In extreme cases, you can try filling them with epoxy (with or without saw dust mixed in) or CA glue. But when in doubt about the stability, I would rather throw it away...

I'm at the point where I'll only work with spalted woods from trusted sources that use a trusted stabilization process. Mark, I include you guys in my small group of folks I trust.

In case anyone wonders what the practical problems seen in most cases with (bad) spalted woods is they buckle when cut into scales from a block. That's not a problem for wa handle work though. Also, whole sections will be powder like and vanish even when hand sanding. For the wa handle makers drilling the center holes can break the wood apart but IMO spalted wood is generally a lot safer to use for wa handles than for westerns.

As I see it the keys to success are to get it stabilized correctly, use sharp drill bits, and new belts/discs to keep the heat down.

Just curious, but for those making handles out of these blocks, do they need to take special precautions when sanding due to spores? Or does the stabilization process kill everything off?

k.

I don't know. If I remember my biology correctly some spores can form a protective shell when subjected to adverse conditions and go dormant.
I go by the assumption that any dust is going to be bad for me to inhale.

Interesting article, having recently worked for the first time with some stabilised wood, I think it was from you in fact, it does work a lot differently to standard wood. Do you have any details around the chemicals used in the process?
I did a bit of mycology at uni and I seem to remember there are broadly 2 types of spalting:
bleaching by White rots that break down the lignin, and
pigmentation spalting where the hyphae grow into the wood cells giving a typically bluish colour.

The lines that form can be where two colonies meet or at the edge of the colony, it has a proper name that I can't remember....

When stabilising burrs will the solution act to glue any loose eyes in place?

What I know about spalting comes from hands on with the wood so my terminology and some information may be deemed as incorrect in regards to some woods.
What I am saying should probably be preceded by a comment like "In my experience....."

Blue spalting typically does not soften or degrade the hardness of the wood. I am not sure why.
Woods around here that can spalt blue are California Buckeye, Pine and rarely Maple. Amboyna burl can sometimes have a blue spalt in the sapwood.

My experience with blackline is it happening when spalting happens in wet conditions and in live trees that are starting to die at the heart.

This last example is a stretch to consider spalting. There may be some fungal activity and decomposing taking place, but not what is normally considered as spalting.
Out at the coast wood that falls in the brackish salt water/fresh water bogs can take on brown, orange and sometimes purple-ish coloring. Some of the coloring can be from minerals absorbed. In the old days they used to throw the myrtle logs into the brackish water and leave it until the wood turned black.